1. Field of the Invention
The invention relates to a method of controlling the temperature of an injection or diecasting mold, the respective temperature of the mold being detected by at lot one sensor and compared to a set point and coolant in particular cooling water, being metered and added through cooling channels disposed in the mold in dependence on any detected overshooting or undershooting of the set point.
2. Background Art
A known method of the generic type is described in U.S. Pat. Nos. 4,354,812 and 4,420,446, coolant pulses being generated, based on a determined average temperature. The drawback of this method resides in that temperature correction can be realized only after several cycles when the conditions in the mold change, such as the pressure or the temperature of the coolant.
In another known method according to German patent 43 09 890, a cooling pulse is emitted at the beginning of the injection cycle and a plurality of cooling pulses are emitted at the end of the injection cycle, based on averaging. This method, too, is accompanied with the drawback mentioned above, the coolant pulses initiated at the end of the cycle having especially negative effects, because They entail an increased heat flow at the end of the cycle, the result of which is the occurrence of cold zones on the surface of the cavity in the vicinity of the cooling channels at the back of it. The melt then encounters a surface of varying temperatures, which forcibly conditions distortion of the product and other lacks of quality. Comparable methods are also described in U.S. Pat. Nos. 5,452,999 and 5,589,114.
Further known prior art teaches an injection mold with three sensors. A sensor in the core is disposed in the wall of the mold directly before the surface of the cavity. This is where a temperature rise is detected after the injection of the hot material to be injected and a short-term decrease after a coolant pulse. However, a renewed temperature rise occurs thereafter, conditioned by the heat entering from outside. Correspondingly, this known method must provide for double cooling each time the adjusted temperature set point is exceeded. This can result in that the temperature of the mold surface decreases clearly below the adjusted temperature set point, reaching the set point necessary for optimum processing only after one or several cycles. This process can recur periodically. In this known method, a second sensor is disposed close to the sprue which is again disposed very close to the cavity. During the regulating process at the same pre-set temperature, the situation arises that the sensor records a temperature rise and triggers the valve to open when the pre-set temperature is reached or exceeded so that a coolant pulse is emitted, the valve closing only when is temperature is no longer reached. Since the corresponding cooling channel may possibly be disposed far away, the heat transfer from the cooling channel to the sensor cannot be synchronous to the cycle, as a result of which the heat extraction by the cooling pulse is noticed too late and as a result of which there is again strong falling short of the pre-set temperature so that the pre-set temperature is reached only after several cycles.